Duolingo finally released a Japanese course, currently only available for iOS. I've been curious what they'd do for that for ages, so I immediately took their placement test to start the course. Background, so you know where I'm coming from: I've been studying Japanese for a hell of a long time, and I'm ... middling at it, been stuck in the intermediate plateau for years because I haven't been able to devote much time to study. Kinda hovering around N3 level, though I have yet to actually pass the N3. But I can get around and have some conversations depending on the topic and read things depending on the vocab. And I've tried a lot of different tools and courses between my formal education at university and my self study.
Also, after I was placed, I found the things I missed were either me making a stupid mistake I did know but failed to input correctly, or me incorrectly guessing what English sentence structure they were intending me to respond with. So instead of going through the rest of the course normally, I tested out of each topic individually, which took me between 1 and 3 tries for each topic. Again depending largely on my luck in guessing what English sentence structure they were looking for. Except for the Olympics topic, which I knew I didn't know much terminology on, so I completed that one normally. It took me around 3 hours to complete everything.
The tl;dr version is that it seems like a decent introduction to Japanese, but the amount of material it covers is approximately the amount we covered in my first month or two of material in the beginning class at college with focus on somewhat different topics. My guess is, based on my experience with the Russian course, that you'll still want to study hiragana and katakana on your own outside of it, but it does provide a relatively gentle introduction to the characters and the entire course is using them, so you'll get practice in reading. If you're looking for just an intro or practice reviewing basics, this would be fine. But don't expect to come out of this course with anything more than basic/travel Japanese. You will sound oddly formal, but understandable, and be able to read... nothing, really, with the amount of kanji and grammar they teach.( some detail )
It's a little difficult for me to compare to their other courses since I haven't completed any others, but also just this course seems sparse on content. As a general Duolingo critique, I'd love to see some of the features that are available in languages like Spanish (or possibly only Spanish?) in other courses, really. Such as the interactive chat bots and speech detection. The speech detection is somewhat spotty in my experience-- I've said things in English to the iOS version that it counted as correct Spanish, but the Android version seemed better at detecting me saying the actual words-- but if they could improve it that would be also nice to have elsewhere. (Russian, please!) Also, give us something else to do with lingots.